This invention relates generally to the art of non-impact asynchronous ink jet printing, and more particularly to electronic driving circuits for ink jet print heads.
The ink jet print heads with which the driving circuit improvement of the present invention is best adapted for use are described in U.S. Pat. No. 3,946,398 -- Kyser, et al. (1976) and co-pending patent application Ser. No. 489,985, filed July 19, 1974, both assigned to the assignee of the present application. A piezoelectric element is associated with an ink jet chamber in a manner that when the element is supplied a high voltage pulse it rapidly reduces the volume of the ink jet chamber, resulting in ejecting a droplet of ink from the orifice with sufficient velocity for it to travel to a recording medium. One such droplet forms a small portion of a character to be printed. A plurality, such as seven or nine, print heads of this type are preferably built as a single structure that is mechanically swept across a recording medium upon which the printing is taking place line by line. At each column of the printing line the appropriate number of the independently controllable ink jet chambers are fired by pulsing their respective piezoelectric elements to eject ink drops therefrom.
Aforementioned co-pending patent application Ser. No. 489,985 describes a basic drive circuitry. Canadian Pat. No. 1,012,198 is based on this pending U.S. application. U.S. Pat. No. 3,857,049 -- Zoltan (1974) describes other driving circuits in ink jet printers. A general approach described therein is to utilize a low voltage control signal pulse to effectively switch a high voltage piezoelectric drive supply on and off in accordance with the pattern of ink droplets that are commanded to be ejected onto the recording medium.
It is a principal object of the present invention to provide such an ink jet piezoelectric element driving circuit that has an improved switching speed, reduced power supply voltage stability requirement and which operates with a reduced amount of power drain.
It is also an important object of the present invention to provide a drive circuit that operates a driven element in a manner to eject droplets of substantially the same size and with substantially the same velocity each time.